The USPS is choosing to reduce service, starting the week of August 5, so that it can save an estimated $2 billion annually. But, according to a letter sent by Grace Meng and other congressmembers to Postmaster General Patrick Donahue Monday, it could actually cost the post office money.

The letter states that the Postal Service is violating “the clearly-stated intent of Congress for the last three decades to continue six-day delivery,” and that it will weaken the Post Office’s business model, negatively impacting postal employees, companies and consumers who depend on Saturday.

“Companies that rely on six-day mail delivery may opt to explore private delivery services. This could very well mean significant mail volume decreases for USPS and further financial hardship,” the letter says. “The Postal Service should look to expand rather than limit the scope of its business.”